This invention pertains to a battery charging apparatus for charging a battery by a rectified output from a magneto generator driven by a primer such as an internal combustion engine and so on.
The battery charging apparatus mounted on a motor bicycle or the like driven by an internal combustion engine comprises a magneto generator driven by the internal combustion engine, a rectifier circuit having input terminals connected to output terminals of the generator and output terminals between which the battery is connected, an output short circuit having on-off controllable switch elements to short the output terminals of the magneto generator when the switch elements are at an on-state and a controller to control the switch elements of the output short circuit in accordance with an output voltage of the battery.
An example of the prior art battery charging apparatus is shown in FIG. 3. A magneto generator 1 generates an AC voltage by being driven by an internal combustion engine mounted on a vehicle such as a motor bicycle or the like. The magneto generator 1 comprises a not shown magnet rotor mounted on a crankshaft of the internal combustion engine and a stator having three phase generation coils Lu through Lw.
A rectifier circuit 2 to rectify an output of the generator 1 comprises a three-phase bridge circuit of diodes Du through Dw and Dx through Dz connected to each other in a bridged manner. AC input terminals 2u through 2w of the rectifier circuit 2 are formed of respective connection points of the diodes Du through Dw for an upper arm of the bridge circuit and the diodes Dx through Dz for a lower arm of the bridge circuit while positive and negative DC output terminals 2p and 2n of the rectifier circuit 2 are formed of the common connection point of the cathodes of the upper arm diodes and the common connection point of the anodes of the lower arm diodes, respectively. The AC three-phase input terminals 2u through 2w of the rectifier circuit 2 are connected to the output terminals 1u through 1w of the generator, respectively, while the battery 3 is connected across the DC output terminals 2p and 2n of the rectifier circuit 2.
A load 4 is connected through a power source switch 5 to both ends of the battery 3. An overvoltage detection circuit 6 serves to detect a terminal voltage of the battery 3 to generate an overvoltage detection signal when an instantaneous value of the detected terminal voltage exceeds a set value.
Thyristors Thu through Thw serve as output shorting switch elements with cathodes thereof commonly connected to the negative output terminals of the rectifier circuit 2 and with anodes thereof connected to the AC input terminals 2u through 2w of the rectifier circuit 2, respectively.
In this example, an output short circuit is formed by the diodes Dx through Dz and the thyristors Thu through Thw. When control signals are applied to the thyristors Thu through Thw, the thyristors having forward voltages applied across the anode and cathode thereof among these thyristors become an on-state and the generator is shorted between the output terminals 1u and 1v, 1v and 1w and 1w and 1u of the U, V and W phases of the generator through the on-state thyristors and the diodes Dx through Dz.
The overvoltage detection circuit 6 comprises a voltage divider circuit formed of a series circuit of a first divider resistor R1, a Zener diode ZD1 and a second voltage divider circuit R2 and connected in parallel to both sides of the battery 3 with the cathode of the Zener diode ZD1 directed to the positive side of the battery 3. The overvoltage detection circuit 6 conducts the Zener diode ZD1 when the instantaneous value of the terminal voltage of the battery 3 exceeds the set value to generate an overvoltage detection signal.
To the connection point of the resistor R1 and the Zener diode ZD1 of the overvoltage detection circuit 6 is connected a base of a PNP transistor TR1 having an emitter connected to the DC output terminals 2p of the rectifier circuit 2 while a collector of the transistor TR1 is connected through resistors Ru through Rw to gates of the thyristors Thu through Thw.
In this example, a switch trigger circuit 7 that applies to the respective thyristors trigger signals for conducting the thyristors Thu through Thw comprises the transistor TR1 and the resistors Ru through Rw. The switch trigger circuit 7 applies the trigger signals to the thyristors Thu through Thw when the terminal voltage of the battery exceeds the set value and thereby the Zener diode ZD1 is turned on to apply the trigger signals to the thyristors Thu through Thw.
In the example of FIG. 3, a regulator circuit 8 having a rectifying function and a voltage regulating function is constituted by the rectifier circuit 2, the output short circuit comprising the low arm diodes Dx through Dz of the bridge of the rectifier circuit 2 and the thyristors Thu through Thw, the overvoltage detection circuit 6 and the switch element trigger circuit 7. The regulating circuit 8 and the generator 1 constitutes the battery charging apparatus.
In the battery charging apparatus shown in FIG. 3, the DC voltage is applied to the battery 3 from the generator 1 through the rectifier circuit 2 to thereby charge the battery 3. The DC voltage (the battery terminal voltage) applied from the rectifier circuit 2 to the battery includes a ripple voltage having a waveform corresponding to that of the AC voltage output from the generator 1. The overvoltage detection circuit 6 applies the trigger signals to the thyristors Thu through Thw when the instantaneous value of the battery terminal voltage including the ripple voltage exceeds the set value.
As the instantaneous value of the terminal voltage of the battery 3 is equal to or less than the set value, the transistor TR1 turns into an off-state because the Zener diode ZD1 of the overvoltage detection circuit 6 is at a nonconductive state and therefore the thyristors Thu through Thw are at an off-state. In these states, the output of the generator 1 is rectified by the rectifier circuit 2 and supplied to the battery 3 so that it is charged. Since the power source switch 5 is closed during the operation of the internal combustion engine, the electric power is supplied from the battery to the load 4.
As the instantaneous value of the terminal voltage of the battery 3 exceeds the set value, the Zener diode ZD1 gets turned on so that the transistor TR1 becomes the on-state because of the base current flowing through the transistor TR1 and as a result, the trigger signals are applied from the battery 3 through the transistor TR1 to the thyristors Thu through Thw. At that time, the thyristors Thu through Thw are conducted while the forward voltages are applied between the anodes and the cathodes thereof and the output terminals of the generator 1 are shorted through either of the conducting thyristors and the lower arm diodes Dx through Dz of the bridge of the rectifier circuit 2. For instance, the thyristor Thu is at the on-state while the output terminal 1u of the generator 1 is at high potential relative to the other output terminals 1v and 1w. At that time, the output terminals 1u and 1v of the generator 1 are shorted through the thyristor Thu and the diode Dy and the output terminals 1u and 1w of the generator 1 are shorted through the thyristor Thu and the diode Dz.
In this manner, since the voltage is never applied from the generator 1 to the rectifier circuit 2 while the output terminals of the generator 1 are shorted, the charging current is prevented from flowing from the rectifier circuit 2 to the battery so that the terminal voltage of the battery is lowered. As the terminal voltage of the battery 3 is equal to or less than the set value, the Zener diode ZD1 becomes the nonconductive state and therefore the transistor TR1 turns into the off-state. Thus, the trigger signals stop being supplied to the thyristors Thu through Thw so that the charging current is again supplied from the rectifier circuit 2 to the battery 3. The terminal voltage of the battery 3 is maintained equal to or less than the set value by repeating this operation.
In the aforementioned battery charging apparatus, when the instantaneous value of the ripple voltage included in the DC voltage applied from the rectifier circuit 2 to the battery 3 exceeds the set value, the Zener diode ZD1 becomes conductive and the trigger signals are applied to the thyristors Thu through Thw so that the voltage regulating operation can be made.
In this case, since the ripple voltage rises abruptly while the revolution of the generator is high, the thyristors Thu through Thw are triggered immediately after the ripple voltage rises and therefore the voltage regulating operation is done at earlier timing. On the other hand, since the ripple voltage rises slowly while the revolution of the generator is low, the thyristors Thu through Thw are triggered in a delayed manner and therefore the voltage regulating operation starts at a delayed time.
Accordingly, it is required for the set value to be set at relatively high level in order to properly control the terminal voltage of the battery when the generator rotates at a high speed, but this sometimes causes the battery terminal voltage to increase when the generator rotates at low speed which delays the start of the voltage regulating operation after the ripple voltage rises.
On the other hand, it is required for the set value to be set at a relatively low level in order to properly control the terminal voltage of the battery when the generator rotates at the low speed, but this disadvantageously prevents the battery from being fully charged because the battery terminal voltage decreases due to the voltage regulating operation starting too early when the generator rotates at the high speed. Particularly, in case that an impedance of the circuit connecting the rectifier circuit and the battery is high, the voltage applied to the battery during the high speed rotation decreases and therefore the battery is insufficiently charged.
As aforementioned, since the prior art battery charging apparatus adversely affects the voltage regulating operation during the steady state of the generator due to the ripple voltage included in the voltage applied from the rectifier circuit to the battery, the circuit constant should be adjusted according to the magnitude of the ripple voltage during the steady operation. However, since the magnitude of the ripple voltage is determined on the winding specification of the generator, the capacity of the battery and the kinds of the load, the circuit constant is required to be set in accordance with the winding specification of the generator, the capacity of the battery and the kinds of the load. This disadvantageously causes the design and manufacture of the battery charging apparatus to be troublesome.
Accordingly, it is a principal object of the invention to provide a battery charging apparatus adapted to charge a battery in a preferable manner without being affected by the winding specification of the generator, the capacity of the battery and the kinds of the load.
In accordance with the present invention, there is provided a battery charging apparatus comprising a magneto AC generator, a rectifier circuit having input terminals connected to output terminals of the generator, an output short circuit having on-off controllable switch elements and shorting the output terminals of the magneto AC generator when the switch elements are at an on state and a controller to control the switch elements of the output short circuit in accordance with the terminal voltage of the battery, the controller including a first switch control section to control the switch elements of the output short circuit to be turned on when the instantaneous value of the terminal voltage of the battery exceeds a first set value, an average voltage detection circuit to detect an average value of the terminal voltage of the battery, a second switch control section to control the switch elements of the output short circuit so as to be turned on when the average value of the terminal voltage of the battery exceeds a second set value and control change-over means to change the controls by the first control section and the second control sections from one to the other so that the switch elements are controlled by the second control section when an electric power is supplied from the battery to the load and so that the switch elements are controlled by the first control section when the load is cut out from the battery.
With the battery charging apparatus constructed in the aforementioned manner, since the switch elements of the output short circuit is controlled by the second switch control section during the steady operation in which the electric power is supplied from the generator to the load, the voltage regulating operation is made to short the output voltage of the magneto generator when the average value of the battery terminal voltage reaches the second set value.
As the load is cut out from the generator when the operation of the generator stops, the voltage regulating operation is done by the first switch control section in accordance with the instantaneous value of the battery terminal voltage during the short period until the generator stops.
As the average value of the battery terminal voltage is detected when the generator is steadily operated and the voltage is so adjusted that the average value thereof never exceeds the set value, the charging voltage for the battery can be steadily controlled without being adversely affected by the ripple voltage having the peak value varying on the changing revolution of the generator.
Since the ripple voltage does not affect the voltage adjustment, the constant of the circuit is not required to be adjusted in accordance with the winding specification of the generator, the capacity of the battery and the kinds of the load, which enables the battery charging apparatus to be manufactured more easily.
Even though the impedance of the circuit connecting the rectifier circuit and the battery is high, the appropriate range of the voltage applied to the battery can be maintained by properly setting the second set value when the generator is driven not only with the low revolution, but also with the high revolution. Thus, the battery can be prevented from being insufficiently charged.
The first switch control section is adapted to directly detect the terminal voltage of the battery across both ends thereof and the average voltage detection circuit serves to detect the average value of the terminal voltage of the battery across both ends thereof when the load is connected through the power source switch to the battery. As the first set value is so set to be higher than the instantaneous value of the terminal voltage of the battery within the range over which the battery and the load are never adversely affected when it reaches the second value, the control by the first switch control section and the control by the second switch control section can be automatically changed. Thus, it will be noted that the power source switch constitutes the control change-over means.
In this case, both of the first and second switch control sections detect the terminal voltage of the battery while the load is connected to the battery, but since the first set value is so set to be higher than the instantaneous value of the battery terminal voltage when the average value of the battery terminal voltage reaches the second value. Thus, it will be noted that while the load is connected to the battery, the average value of the terminal voltage detected by the average voltage detection circuit exceeds the second value so that the second switch control section turns on the switch elements of the output short circuit before the first switch control section turns on the switch elements of the output short circuit. In this manner, the second switch control section controls the switch elements of the output short circuit on the steady operation of the generator whereby the voltage adjustment operation is made so that the average value of the battery terminal voltage can be maintained equal to or less than the second set value.